Mails scanned by SpamAssassin + ClamAV (both invoked by Amavisd) will be re-injected into Postfix queue (by Amavisd, of course), and Postfix will invoke proper transport to deliver them, in this stage, the transport is usually set to "dovecot" which defined in /etc/postfix/master.cf. Transport "dovecot" executes Dovecot MDA (mail deliver agent) program to deliver emails.

That's why i asked for Dovecot logs.

I suggest turning on debug mode in Dovecot, then try sending a testing email again and paste related log in Dovecot log files.Reference: